Alternating current generator



y 1945- I K. s. DUNLAP ETAL 2,375,131 I ALTERNATING CURRENT GENERATOR IFiled Sept. 2 1942 FIG! IA'. LOVELL Y .r. MALL/NA ATTORNEY /NVENTORSreeds actuating mechanism, shown in normal flexed position.

3 PatenteJMay 15,1945

- UNITED STATES i PATENT Torn cs 2,376.13}

KermltS. Dunlap, summit, George a. KelsalL- Belleville, andClarenceLInvell, Summit, N. J.,

and Rudolph F. Malllna, Hastingson Hudson,

N. Y., ,assignors to-Bell Telephone Laboratories, I

Incorporated, New New York 4 York, N. Y., a. corporation or aADplicaflon September 26, 1am, sci-mm. 459,182

4 Claims. for 111-409) This invention relates to alternating, currentgenerators of the type in which the operationvof difierently tunedvibrative elements between the poles of a magnet generate alternatingcurrent in a coil of frequencies corresponding to those plates attheirfront edges being formed diag-.

onally for the purpose of clamping different length portions of thereeds so as to obtain diiierent periods of frequencies in the operationof these reeds.

The object of this invention is to improve the construction of such agenerator and increase the strength of the signals generated by theoperation of the vibrative elements.

A ieatureof the invention is the provision of i an unsymmetrical magnetstructure to furnish the saturating flux while field in the gap.

Another feature is the provision of a magnetic stopping bar attached tothe upper pole-piece of the magnet which limits the flexing amplitude ofthe reeds while furnishing a means of saturating theunused reeds. 1

Another feature is the provision of a tapered gap formed in the magnetassembly to produce better wave form in the low frequency signals whilecontrolling the output voltage characteristics.

Another feature is the increase of the efiective magnet length by theuse of brass plates assembled with the reeds to form a unit structure.

Another feature is the use of a magnetic material for the constructionof the reeds heat treated in a magnetic field.

Other novel features and advantages will appear from the followingdescription and by the maintaining a balanced claims appended thereto,reference being had to the accompanying drawing in which:

Fig. 1 is an assembly view of the generator shown in perspective;

Fig. 2 is a plates and reeds assembly;

Fig. 315 an exploded view of Fig.2; Y I V Fig. 4 is a partial assemblyview showing the view in perspective of the brass the reeds being 5 Fig.5 is a view similar to Fig. 4 shown with a combination of reedsfreleasedso as to permit the vibration of these reeds between the pole-' pieces01' the magnet; and

Fig. 6 is a front assembly view shown with the reeds in non-tensionedposition.

According to the alternating current generator of this invention, apermanent magnet is formed or the complemented sections A and B, shownin Figs. 1, 4., 5 and 6,,having registering portions forming a recessfor a coil and a gap. These sections .are constructed of a three percentchrome steel, permitting a relatively narrow gap producing a flux source,suflicient to load the reed material to maximum capacity and therebyobtaining the maximum signalto which the reeds are capable. Thevibrative reeds R1, Ra, R3 and R4 as shown in Fig. 3, are constructed bypunchingtapered projections of difierent lengths from a sheet .of amaterial comprising substantially 34 to 50 per cent nickel, to 40 percent iron,

20 to per cent cobalt and 1 to e per cent Incv lybdenum heat treated byplacing the reeds positioned on a permanent magnet in a furnace, raisingthe temperature of the furnace to approximately 600 0., allowing themagnet and reeds to remain therein for approximately one hour at'thattemperature and allowing the fur nace to cool to 'room temperature.

Applicants have discovered that partial annealing of the reeds in amagnetic field had the efiect of decreasing the hysteresis losses of thematerial without injury to its mechanical properties, while themechanical dissipating resistance and the eddy current losses .of thismaterial have been found in actual use to be negligible,

resulting in a relatively high'signal strength.

The plate portion ill with which the reeds R1, R2, etc. are formed,issecured as by brazing between brass plates ii and I2 using hard solderin the form of foil F and Fl. This assembly is afterward clamped betweenthe magnet sections A'and B, as by a plurality of rivets it, in additionto a plurality oi screws, not shown, fitted in holes l4 serving tosecure the entire assembly on a. mounting 15 shown partially in Figs. 4

and 5, while the use of brass plates H and i2 considerably increases theefiective length of the ;magnet.,' The vibrative elements thus assembledextend through an opening ina core l6 of insulating material shown inFigs. 5 and 6 on which the coil I1 is wound, the core i6 being providedwith a vplate 18 of insulating material having metallic terminals in theform of eyelets I9 and 20' serving to connect the ends'of the coilcapable.

wire to terminals 2| and 22 in turn connected to the telephone line in aterminal bank (not shown).

The front disposed end portion of magnetic sections A and B whenassembled as shown in Figs. 1, 4, 5 and 6 form a tapered gap betweenwhich the free ends of the vibrative reeds R1,

Ra, Ra etc., are operated, these reeds being disposed in relation to thechange of space between the pole-pieces with the reed R5 having thelowest tuned frequency operating at the greatest gap distance.

The reeds R1, R2, R3, etc., as shown in Figs. 4 and 5 extend inoperative relation with lever members at LM and when flexed undercontrol of digit key members (not shown) are moved in abutting relationwith a plate 25 of magnetic material secured as by screws 23 to themagnet section A, the release of such reeds being effected inpredetermined combinations by lever members LM in cooperation with apawl-like member 26, the operation of which by lever members LM in pairscausing the release of reeds associated with that pair of lever membersto permit the vibration of the reeds thus released, while the reedsassociated with the non-operated arms LM remain in abutting relationwith the bar 25, these operative conditions being indicated in Fig. 5.

According to this construction, the reeds as above mentioned, which arenot operated during the transmitting of a particular signal are heldagainst the magnetic abutting stop plate 25 to become saturated withmagnetic flux, thus having the effect of decreasing the coil inductanceand eliminating the shunt paths that are offered by unsaturated reeds tothe alternating flux in the vibrating reeds. Such construction has beenfound to raise the signal levels by several decibels over those knownwithout decreasing the number of effective signal transmittingoperations of the reeds, while the unsymmetrical construction of the gapformed by the magnetic sections A and B has been found to furnish thesaturating flux and still maintain the balanced field in the gap whichis necessary for good signal wave form.

The reeds R1, R2, R3, etc. are flexed by the operation of theiractuating arms LM with emplitudes that produce approximately equal fiberstresses in all reeds, thus enabling each reed to vibrate at its maximumsafe amplitude and to generate the maximum voltage of which it is Thelowest frequency reeds vibrate at the largest amplitudes which in turnis allowed by the tapered width of the magnetic gap.

What is claimed is:

1. In an alternating current generator, a twoelement permanent magnethaving registering securing portions, 8. reed assembly 01 resilientmaterial secured between said portions, one of said elements having itsfree end extending in overlapping relation with the adjacentiy disposedend of the other of said elements, said elements having portions forminga tapered gap transverse of said reeds, and means carried by one of saidelements forming part of the magnetic circuit thereof and serving as astop for limiting the flexing movement of the said reeds.

2. An alternating current generator comprising a permanent magnet madeof two complemental sections, a plurality of reeds of resilient materialand brass plates assembled to form a unit riveted between said sections,one end of one of said sections extending in overlapping relation overthe ends of the other of said sections, and a plate of magnetic materialsecured to the overlapping end of said sections for engagement with thefree ends or said reeds when flexed.

3. In an alternating current generator, a coil, a permanent magnet madeof two independent rectangularly shaped sections having securingportions at similarly disposed ends and their opposite ends forming atapered gap and a mounting for said coil, a reed assembly, said reedsbeing resilient and having their free ends extending through said coilfor vibrative operation in the gap between said sections, a plate .ofmaghetic material carried by one of said sections against which saidreeds are tensioned, and means for releasing said reeds in predeterminedcombination to cause their vibration, the nonreleased reeds remaining incontacting relation with said magnetic plate.

4. In an alternating current generator, a persections, a coil having ahollow core and a termanent magnet constructed of complemental terminalplate for connecting the wire ends of said coil, said sections havingportions forming when assembled a recess for said coil and a taperedgap, a pair of brass plates, a. plurality

